1. Field of the Invention
This invention relates to an automatic transmission torque converter lock-up clutch actuated by a pressurized hydraulic control circuit.
2. Description of the Prior Art.
German patent Document DE-PS 31 21 749 discloses a method to control a clutch located between a driving shaft and a driven shaft and a control system for a hydrokinetic torque converter lock-up clutch. The method of control includes detecting a deviation from the speed of the driving shaft using a sensor and controlling the difference in speed of the driving shaft and driven shaft such that this speed difference is greater than the detected deviation in the speed of the driving shaft.
This known method of control enables the difference, resulting from slippage, in the speed of the driving and driven shafts to be kept greater than the irregularity after a certain irregularity has been detected in the driving shaft. Undesirable effects of torsional vibrations of an internal combustion engine on the hydrokinetic, mechanical compound transmission can be avoided by this control technique.
The method of control described in the '749 document has the disadvantage of requiring a relatively complex microprocessor in order to calculate a relatively great slippage, corresponding to the respective difference in speeds of the driving shaft and driven shaft and to provide a corresponding control variable if irregularity in speed of the driving shaft results. The control system includes a lock-up clutch control valve to which pressurized hydraulic fluid is applied under line pressure, which is regulated by an associated pressure modulating valve in the form of a pulse-width modulated PWM solenoid valve, electrically triggered directly by a microprocessor.
The microprocessor also triggers a lock-up clutch, which operates at different states depending on the shift positions of the compound transmission.
German patent Document DE-PS 31 30 871 discloses a control system for a torque converter lock-up clutch supplied with pressurized fluid through a hydraulic circuit in a compound transmission. Hydraulic fluid at line pressure is supplied to a lock-up clutch pressure control valve and is supplied selectively to an application pressure chamber or a release pressure chamber as a function of the operating states by the action of control pressure. The lock-up clutch pressure control valve consists of a valve body, having three control lands located in a valve cylinder, held by a valve spring in a starting position where it conveys line pressure between control lands 2 and 3 to the release pressure chamber, and connects the application pressure chamber between control lands 1 and 2 to a cooler. A control pressure, which is controlled by an electromagnetic valve, is applied at control land 3 to move the valve body against the force of the spring into its shift-up position, where it conveys line pressure between control lands 1 and 2 to the application pressure chamber and connects the release pressure chamber to the cooler.
The control system of the '871 document has the disadvantage that, in addition to the normal lock-up clutch control valve, it requires a lock-up clutch pressure control valve on which a pressure reducing valve and an electromagnetic valve also operate. The production costs are therefore relatively high.
German patent Document DE-OS 38 18 102 discloses a control device for a torque converter lock-up clutch operating in a compound transmission and actuated by pressurized hydraulic fluid. In the control system of the '102 document, a lock-up clutch pressure control valve consists of a valve body having three control lands arranged in a valve cylinder, the valve being held in its starting position by a valve spring. An electromagnetic valve produces, on one end of the valve spool, a control pressure, which varies as a function of the torque transmitted. The necessary torque transmission capacity is determined by comparison of the driving shaft speed and the driven shaft speed, and a corresponding magnitude of control pressure stored in a memory is associated with a torque capacity in order to allow desired slippage.
Here also, the microprocessor must provide additional application and release functions to the lock-up clutch.
German patent Document DE-PS 31 03 838 discloses a control device for a lock-up clutch of a hydrokinetic torque converter supplied with pressurized hydraulic fluid in a compound transmission. Hydraulic fluid is supplied at line pressure to a lock-up clutch control valve, and is supplied selectively to an application pressure chamber or a release Pressure chamber as a function of operating states by the effect of control pressure. The lock-up clutch control valve includes a valve body and four control lands, located in a valve cylinder and held by a valve spring in a starting position, where it directs line pressure between control lands 1 and 2 to the release pressure chamber and connects the application pressure chamber through a line to a cooler. Hydraulic fluid is directed also between control lands 2 and 3 to an outlet, where control pressure is applied at control land 4 to move the valve body against the force of a valve spring to its shift-up position, where it supplies line pressure between control lands 2 and 3 through the cooler to the application pressure chamber of the torque converter. The release pressure chamber is connected between control lands 1 and 2 to an outlet.